Photoemission study of interface formation between ytterbium and tris-(8-hydroxyquinoline) aluminum

Interface formation between Yb and tris-(8-hydroxyquinoline) aluminum (Alq3) was systematically investigated using X-ray and ultraviolet photoelectron spectroscopies (XPS and UPS). The interface formation depended critically on the way it was prepared. For the case of Yb deposited on Alq3, the XPS results revealed staged interface reactions. Upon oxygen exposure, the effect of Yb/Alq3 interaction can be eliminated. By proper oxidation, the interface of Yb/Alq3 can form an ohmic contact, leading to good electron injection. On the other hand, when Alq3 was deposited on Yb, it was considered that the large ratio of Yb to Alq3 resulted in substantial charge transfer to the Alq3 molecules to form even the trivalent Alq3−3 radical anions.